Electrical apparatuses often include optional accessories which are provided on a plug-in circuit card and attached to the apparatus by inserting the card into a connector on a motherboard within the apparatus. For example, many computer designs have processor and, or memory boards and the like which are connected to the computer by insertion into a connector on a motherboard.
Connections between the card and motherboard are made by mating a connector on the card to a corresponding connector on the motherboard. As circuit complexity increases, the number and density of pins and sockets on the connectors increases. As the density increases, the accuracy with which the card must be positioned relative to the connector on the motherboard also increases. To provide this accuracy, card guides are normally positioned relative to the connector on the motherboard. The circuit card slides in the card guide which provides the proper alignment during card insertion.
The card guides are also used for providing additional ground connections. Typically, the edge of the circuit card that slides in the guide has a plated section which is connected to the ground bus on the circuit card. Spring loaded protrusions on the card guide engage this plated section. The protrusions in question are connected to the ground bus of the motherboard.
In prior art designs, the card guide utilizes the same set of protrusions both for positioning the card relative to the motherboard and for making the ground connections. To provide sufficient accuracy in aligning the circuit card, the card guide must present a substantially rigid "slot" to the circuit card. The slot must have a width which is very close to the thickness of the circuit card. However, to provide the electrical connections described above, the protrusions must contact the card with sufficient force to assure a good electrical connection.
To accomplish both of these goals, prior art devices have employed spring loaded protrusions disposed on each side of the slot. The protrusions are designed such that the spacing between opposing protrusions is less than the thickness of the circuit card when no circuit card is inserted in the slot. When the circuit card is inserted in the slot, the protrusions are forced apart by the insertion motion. The circuit card is then caused to slide between the protrusions until the connectors are engaged.
Since the protrusions must restrict the lateral motion of the circuit card relative to the slot, the force generated by the protrusions on the sides of the circuit card must be sufficient to prevent the circuit card from moving in a lateral direction. Such a force is significantly greater than the force needed to assure electrical contact between the protrusions and the plated region on the circuit card. In fact, the force required to make prior art card guides function properly is so large, that it hampers the insertion and removal of the circuit cards.
Broadly, it is the object of the present invention to provide an improved printed circuit card guide.
It is a further object of the present invention to provide a circuit card guide having reduced insertion force than prior art devices while providing ground connections for the circuitry on the card.
These and other objects of the present invention will be apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.